id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
1092	Simulation of tank model fails	krsta	krsta	"From: owner-openmodelicainterest@ida.liu.se
[mailto:owner-openmodelicainterest@ida.liu.se] On Behalf Of Vasaiely, Parham
Sent: den 23 mars 2009 14:24
To: OpenModelicaInterest@ida.liu.se
Subject: 

Hello OpenModelica users,

we have discovered some behavior of OMC that we didn't expect: When we
simulate the 2 tanks model (OMNotebook chapter 12.1 ""Modeling a Tank
System"", the part ""Object Oriented Component-based (p. 386)"" than the last
part ""7. Simulation of TanksConnectedPI"") from startTime greater than 0 then
OMC (version 1.4.5) doesn't return the results starting form the startTime
but results starting from startTime=0. Here are our commands and resulting
data:

*Note: ""numberOfIntervals"" is used for integer time steps.

{{{
simulate(Demo.TwoTanks.TanksConnectedPI, startTime=0, stopTime=400,
numberOfIntervals=400, tolerance=1e-4)

plot(tank1.h)

T -> tank1.h
0 -> 0
1 -> 0.02
2 -> 0.04
3 -> 0.06
4 -> 0.08
5 -> 0.1
6 -> 0.12
7 -> 0.14


simulate(Demo.TwoTanks.TanksConnectedPI, startTime=5, stopTime=400,
numberOfIntervals=395, tolerance=1e-4)

plot(tank1.h)

T -> tank1.h
5 -> 0 (THIS SHOULD BE 0.1)
6 -> 0.02 (THIS SHOULD BE 0.12)
7 -> 0.04 (THIS SHOULD BE 0.14)
}}}

You can see more difference by using a start time grater than 100.

Is it a correct behavior or a bug of the OMC?
-----------------
Here is the Modelica code for the two tank model:
{{{
package TwoTanks
  model TanksConnectedPI
    LiquidSource source(flowLevel = 0.02);
    Tank tank1(area = 1);
    Tank tank2(area = 1.3);
    PIcontinuousController piContinuous1(ref = 0.25);
    PIcontinuousController piContinuous2(ref = 0.4);

  equation 
    connect(source.qOut,tank1.qIn);
    connect(tank1.tActuator,piContinuous1.cOut);
    connect(tank1.tSensor,piContinuous1.cIn);
    connect(tank1.qOut,tank2.qIn);
    connect(tank2.tActuator,piContinuous2.cOut);
    connect(tank2.tSensor,piContinuous2.cIn);
  end TanksConnectedPI;
  model Tank
    ReadSignal tSensor ""Connector, sensor reading tank level (m)"";
    ActSignal tActuator ""Connector, actuator controlling input flow"";
    LiquidFlow qIn ""Connector, flow (m3/s) through input valve"";
    LiquidFlow qOut ""Connector, flow (m3/s) through output valve"";
    parameter Real area(unit = ""m2"") = 0.5;
    parameter Real flowGain(unit = ""m2/s"") = 0.05;
    parameter Real minV = 0,maxV = 10;
    Real h(start = 0.0, unit = ""m"") ""Tank level"";

  equation 
    assert(minV >= 0, ""minV - minimum Valve level must be >= 0 "");
    der(h) = (qIn.lflow - qOut.lflow) / area;
    qOut.lflow = limitValue(minV, maxV,  -flowGain * tActuator.act);
    tSensor.val = h;
  end Tank;
  connector ReadSignal ""Reading fluid level""
    Real val(unit = ""m"");
  end ReadSignal;
  model PIcontinuousController
    extends BaseController(K = 2, T = 10);
    Real x ""State variable of continuous PI controller"";

  equation 
    der(x) = error / T;
    outCtr = K * (error + x);
  end PIcontinuousController;
  model LiquidSource
    LiquidFlow qOut;
    parameter Real flowLevel = 0.02;

  equation 
    qOut.lflow = if time > 150 then 3 * flowLevel else flowLevel;
  end LiquidSource;
  connector LiquidFlow ""Liquid flow at inlets or outlets""
    Real lflow(unit = ""m3/s"");
  end LiquidFlow;
  function limitValue
    input Real pMin;
    input Real pMax;
    input Real p;
    output Real pLim;
  algorithm 
    pLim:=if p > pMax then pMax else if p < pMin then pMin else p;
  end limitValue;
  partial model BaseController
    parameter Real Ts(unit = ""s"") = 0.1 ""Time period between discrete
samples"";
    parameter Real K = 2 ""Gain"";
    parameter Real T(unit = ""s"") = 10 ""Time constant"";
    ReadSignal cIn ""Input sensor level, connector"";
    ActSignal cOut ""Control to actuator, connector"";
    parameter Real ref ""Reference level"";
    Real error ""Deviation from reference level"";
    Real outCtr ""Output control signal"";

  equation 
    error = ref - cIn.val;
    cOut.act = outCtr;
  end BaseController;
  connector ActSignal ""Signal to actuator for setting valve position""
    Real act;
  end ActSignal;
end TwoTanks;
}}}
-----------------


Thanks for your support!
Pharham"	defect	closed	high				invalid		krsta